I think you'll need to wait till it attaches itself to something, then you can glue it to a bigger rock. If you try to glue the shroom itself, it will probably slime off and float away. Try and get some netting (I use old orange bags and cut them in small pieces) and a plastic container. Cut small holes in the sides of the container, and put some crushed coral in the bottom, then place the netting over the top, after a couple of week, the shroom should attach to some of the CC and then you can glue it to something.